The present invention relates to a method for manufacturing photosensitive materials and particularly a method of manufacturing photothermographic materials by bead coating.
Simultaneous multiple bead coating is used for manufacturing a photosensitive materials to apply multiple layers of photosensitive materials to a web. A multiple slide hopper shown in U.S. Pat. No. 2,761,791 is one of well-known coating apparatus for making simultaneous multiple coating through a bead of multiple layers formed between a lip of the multiple slide hopper, where a layered coating liquid flows by gravity on a inclined slide surface of the hopper, and a running web.
This slide bead coating can easily control a coating thickness by adjusting a web running speed and a feeding rate of coating liquid, and is suitable way for having thin layer coating which gives good photosensitive resolution and for making simultaneous multiple coating which increases productivity and decreases possibility of coating defects.
Slide bead coating, however, occasionally causes streak-like coating defect, which results in streak-like unevenness of optical density when the coated photosensitive product is used. It seems to happen more in the coating of photothermographic materials, which lowers quality of the product.
An object of the invention is to provide a coating method for manufacturing photosensitive materials, especially manufacturing photothermographic materials, with free from streak-like coating defect.
To accomplish the object studies were made and it is found that when the outer side layer includes materials capable of increasing optical density such as toner, streaks become more visible, and the streaks defect is restrained when meniscus curvature of upper side bead becomes less than a specified value. More specifically, the followings are inventions as described in the claim.
Method for manufacturing photosensitive materials comprising steps of: forming a liquid multilayer composite of a plurality of distinct layers on a slide hopper and; forming a bead of the liquid multilayer composite between a lip of the slide hopper and a running web so that an upper meniscus curvature of the bead is less than 7.2 mmxe2x88x921.
Method according to above, wherein the liquid multilayer composite includes a liquid photosensitive layer containing a silver salt of organic acid and a hydrophobic polymer latex and a liquid non-photosensitive layer containing a water-soluble polymer.
Method according to those two of above, wherein the upper meniscus curvature of the bead being less than 7.2 mmxe2x88x921 is accomplished by selecting a proper value of clearance between the web surface and the lip of the slide hopper and a proper value of pressure in a lower side of the bead.
The proper value of clearance ranges from 0.10 mm to 0.40 mm and the proper value of pressure ranges from xe2x88x92100 Pa to xe2x88x92700 Pa. The coating liquid of the photosensitive layer has thixotropy that a viscosity of the liquid shows from 300 mPaxc2x7s to 30,000 mPaxc2x7s at shear rate 0.1/s and from 1 mPaxc2x7s to 100 mPaxc2x7s at shear rate 1000/s.